It is known that SO2 is more soluble in water than many other components of feed gas streams. For example, measured at 1.013 bar 0° C., the solubility of SO2 in water is 228 g/L whereas the solubility of carbon dioxide and hydrogen sulfide in water is 3.369 g/L and 7.100 g/L, respectively.
The solubility of SO2 in many other pure solvents has also been widely studied. See, for example, Fogg and Gerrard, 1991 (Solubility of Gases in Liquids, John Wiley and Sons, Chichester, U.K.) for a summary of the literature solubility data of SO2.
Regenerable absorbents can be used to remove SO2 from feed gas streams. Typically, a lean aqueous medium comprising the absorbent is exposed to a SO2 containing feed gas stream, and then SO2 is absorbed by the medium producing a SO2 lean gas stream and a spent absorbing medium. Removal (recovery) of the absorbed SO2 from the spent absorbing medium to regenerate the aqueous medium and to provide gaseous SO2 is typically effected by gaseous stripping using steam generated in situ.
Amine-based absorbents can be used for SO2 removal. See, for example, U.S. Pat. No. 5,019,361 which discloses the use of an aqueous absorbing medium containing a water-soluble half salt of a diamine. U.S. Pat. No. 7,214,358 discloses the use of an aqueous absorbing medium containing a water-soluble half salt of a diamine and an elevated level of heat stable salts (HSS). Physical solvents can also be used as SO2 absorbents.
Commercially available steam-regenerable SO2 capture technologies include those that rely on chemical solvents or physical solvents, such as Cansolv DS™ (amine-based absorbent-containing chemical solvent), Labsorb™ (inorganic absorbent-containing chemical solvent), ClausMaster™ (non-aqueous physical solvent), and Sea water process (chemical solvent).
Use of a combination of solvents has also been disclosed.
Indian Patent Application No. 2381/DEL/2006 describes a process for the removal of SO2 using a solvent blend comprising chemical and physical solvents.
US20130039829 describes a process for the capture of sulfur dioxide from a gaseous stream utilizing a regenerable diamine absorbent comprising a diamine and a weak organic acid, such as formic acid.
The energy required for regenerating absorbing medium in a SO2 removal process, in particular the energy required for stripping absorbed SO2 from absorbing medium, accounts for a significant portion of the operating cost of SO2 removal from a feed gas. For example, the net present value of the existing SO2 capture technologies is strongly dependent on steam cost. Therefore, there remains a need to reduce regeneration energy consumption in processes for removing SO2 from a gas stream.